1. Field of the Invention
The present invention relates to a device for detecting an angular displacement relative to absolute space by utilizing the inertia of a liquid and, for example, to an angular displacement detecting device suitable for use in detecting an image shake which may occur during photography using a camera.
2. Description of the Related Art
A conventional angular displacement detecting device of this type is basically constructed as described below in detail, as disclosed in U.S. Pat. application Ser. No. 637,532, filed on Jan. 4, 1991, and Japanese Laid-open Patent Application Nos. Hei 2-82165 and Hei 2-102414. The construction will be explained with reference to FIGS. 1 to 3.
As shown in these figures, the conventional angular displacement detecting device comprises a base 1 to which individual parts for constituting the device are secured in position, and a tubular casing 2 serving as a sealed liquid container having a chamber in which a floating body 3 and a liquid 4 are sealed. The tubular casing 2 has a groove 2a which is formed in its inner wall so as to securely engage with a floating-body support 14 having a U-like cross section as shown in detail in FIG. 3. The floating body 3 has magnetic characteristics, and is supported for rotation about an axis 3a by the floating-body support 14. Mirrors 9 are respectively secured to one pair of opposed side faces of the central block of the floating body 3, and each of the mirrors 9 is covered by a mask 10 having a slit 10a. Arms 3b extend from the other pair of opposed side faces of the central block, respectively. The floating body 3 is constructed so as to maintain the balance of buoyancy in the liquid 4 by making their specific gravities coincide with each other.
It is to be noted that the liquid 4 sealed in the tubular casing 2 is a transparent liquid.
A light emitting element (IRED) 5, which is adapted to emit light by energization, is secured to the base 1 via a light-emitting element carrier 7. A light receiving element (PSD) 6 utilizes a photoelectric conversion device whose output varies with the position where light is received, and is fixed to the base 1 via a light-receiving-element carrier 8. The light emitting element 5 and the light receiving element 6 constitute optical angular displacement detecting means of the type which transmits light by means of either of the mirrors 9 secured to the opposed side faces of the central block of the floating body 3. A light guide portion 7a is formed on the light-emitting element carrier 7 for guiding light emitted from the light emitting element 5, and a mask 10' is secured to the distal end of the light guide portion 7a. The mask 10' has a slit 10a' identical to the slit 10a of the mask 10. Since light transmission is effected through the tubular casing 2, the whole or a predetermined portion of the tubular casing 2 is formed of a transparent material.
A pair of yokes 19 and 20 is disposed in such a manner as to produce a magnetic field action for holding the floating body 3 having the magnetic characteristics in a fixed position, i.e., in a position where the floating body 3 takes the shown attitude. Opposed ends of the respective yokes 19 and 20 are spaced apart from each other along the diameter of the tubular casing 2 as shown in FIG. 1. A yoke 21 is interposed between the other end portions of the yokes 19 and 20, and a solenoid coil 22 is fitted onto the yoke 21. The above-described arrangement allows a magnetic circuit to be formed by the yokes 19, 20 and 21 and the floating body 3, and a magnetic force is imparted to the floating body 3 by the magnetic force produced by the solenoid coil 22.
The above-described rotatable supporting of the floating body 3 is accomplished in the following manner. As shown in FIG. 2 in cross-sectional form, a rotary shaft 11 extends through the central block of the floating body 3 in the vertical direction, and a pivot 12 having an outwardly pointed end is press-fitted into each of the top and bottom ends of the rotary shaft 11. Pivot bearings 13 are secured respectively to the end portions of the upper and lower arms of the U-like shape of the floating body support 14 in such a manner that they are opposed to each other in the inward direction. The floating body 3 is supported by the engagement between the pointed ends of the pivots 12 and the corresponding pivot bearings 13.
A lid 15 is bonded to the tubular casing 2 in a sealed manner by a known art utilizing a silicone adhesive or the like. A packing rubber 16 is sandwiched between a pressure disk 17 and the lid 15, and is fixed by screws or the like.
In the above-described arrangement, the floating body 3 is constructed so that the balance of buoyancy in the liquid 4 can be maintained as described previously in order to prevent a substantial load from acting on the pivotal axis of the device by the influence of gravitation.
According to the above-described arrangement, even if the tubular casing 2 rotates about the rotational axis 3a, an inner portion of the liquid 4 does not move owing to inertia and, therefore, the floating body 3 which is in a floating state does not rotate. As a consequence, the tubular casing 2 and the floating body 3 rotate about the rotational axis 3a with respect to each other. This is the principle of the present inventive device for detecting a relative angular displacement, and the relative angular displacement can be detected by the optical detecting means utilizing the light emitting element 5 and the light receiving element 6.
In practice, a flow is produced in the inner portion of the liquid 4 by the influence of the wall surface of the tubular casing 2, and the flow applies a viscosity force to the floating body 3. The influence of the flow, however, can be minimized by appropriately selecting factors such as the distance between the wall surface and the floating body 3 and the viscosity of the liquid 4.
In the device having the above-described arrangement, detection of an angular displacement is accomplished in the following manner.
Light emitted from the light emitting element 5 through the light guide 7a illuminates the floating body 3, and light reflected by an illuminated one of the mirrors 9 reaches the light receiving element 6. As described above, the mask 10' is secured to the distal end of the light guide 7a, while the mask 10 is secured to each of the mirrors 9 of the floating body 3. Accordingly, the light is approximately collimated by the slit 10a of the mask 10 during light transmission, whereby a sharply focused image (slit image) is formed on the light receiving element 6.
The tubular casing 2, the light emitting element 5 and the light receiving element 6 integrally move since all of them are secured to the base 1. If a relative angular displacement occurs between the tubular casing 2 and the floating body 3, the slit image on the light receiving element 6 will move by an amount corresponding to the relative angular displacement. Accordingly, the light receiving element 6, which utilizes a photoelectric conversion device whose output varies with the position where light is received, produces an output substantially proportional to the positional displacement of the slit image. It is, therefore, possible to detect the angular displacement of the tubular casing 2 by utilizing such an output as information.
In the case of the angular displacement detecting device having the above-described arrangement, since the floating body 3 is not subjected to an external force, the attitude of the floating body 3 cannot be restricted. As a result, it might be considered impossible to ensure that the slit image is positioned within the measurement range of the light receiving element 6. However, if, for example, the above-described solenoid coil 22 is used to exert a weak magnetic field action on the floating body 3, the magnetic field action can be made to act as a spring force which produces a force locating the floating body 3 at the steady position shown in FIG. 1.
The spring force exerted on the floating body 3 by the magnetic field action is theoretically a force which maintains the floating body 3 in a fixed attitude with respect to the tubular casing 2, i.e., a force which acts to move the floating body 3 integrally with the tubular casing 2. If such spring force is excessively strong, the tubular casing 2 and the floating body 3 will move integrally, thus resulting in the problem that a relative angular displacement required for a desired angular displacement is not produced. However, if the magnetic field action is made sufficiently small with respect to the inertia of the liquid 4, it is possible to realize an arrangement capable of responding to an angular displacement of relatively low frequency as well.
In general, to improve the detection sensitivity of such an arrangement, it is indispensable that the specific gravity of a floating body be made to coincide with that of a liquid, thereby preventing a substantial load from acting on the pivotal axis of the device by the influence of gravitation. However, even in a case where the specific gravity of the floating body is macroscopically coincident with that of the liquid, if microscopic variations exist in the specific gravity of the floating body, angular moment corresponding to .DELTA..rho..times.V.times.l.times.g will be produced about the pivotal axis, where .DELTA..rho. is the difference in the specific gravity, V is the volume of a portion where the microscopic variations exist, l is the distance from the pivotal axis to the center of gravity and g is gravitational acceleration. As is apparent from the principle of the present invention, a force which acts to locate the floating body at a steady position is applied thereto as a spring force by utilizing the magnetic field action produced by a solenoid coil.
Accordingly, if the angular moment about the pivotal axis due to the microscopic variations in the specific gravity of the floating body is greater than the spring force, the floating body will rotate by the influence of gravitation. If the rotation of the floating body is to be inhibited, it is necessary to increase the spring force. However, if the spring force is increased, the floating body will move integrally with the tubular casing, thus resulting in the problem that a relative angular displacement required for a desired angular displacement is not produced. For this reason, since the detection sensitivity becomes higher as the spring force is made weaker, it is desired to minimize variations in the specific gravity of the floating body.